Remote control system



Filed Aug. 5`, 195o `1*.A L. sTuRciEs REMOTE CONTROL SYSTEM 2 SHEETS-SHEET 1 INVENTOR.

THOMAS L. STURGES n M b' ATTORNEYS Dc- 16, 1952 T. l.. sTuRGEs 2,622,134

REMOTE CONTROL SYSTEM Filed Aug. 5, 195o 2 SHEETS-SHEET 2 I N VEN TOR. THOMAS L. STURGES ATTORNEYS Patented Dec. 16, 1952 UNITED STATES PATENT GFFICE 14 Claims.

My invention relates to remote control systems for electrical machines and has for an object the provision of a system which is -simple and reliable and which requires buta single pair of conductors for supply of power current to a distantly located machine and for the supply over the same pair of conductors of control currents of a different character to effectuate precise control functions at theL distantly located electrical machine.

Heretofore various systems have been provided for the remote control of electrical apparatus in which supervisory control signals have been carried by power conductor-s to remotely located receiving stations. But systems of the foregoing character have in general required special coupling devices both at thev transmitting and receiving ends of the power conductors, together with relatively expensive apparatus for generating supervisory signals of a character substantially differing from those normally carried by the power lines.

In carrying out the present invention in one form thereof, a transfer switch at a remote location may be operated from one position to the other as determined by the position of a. selector switch in conjunction with the energization of a relay located at said remote station. Such transfer switch functions as a power-controllingA contactor for electrical machinery. Further in accordance with the invention, the selector switch is connected between a pair of conductors eX- tending from the control station to the remotely located station. The selector switch may be operated selectively to apply to the pairof conductors direct current of one polarity or the other, or to apply alternatingl current thereto, to provide for selective response of theV transfer switch and the relay to control and power currents.

Further in accordance Vwith the invention, the relay located at the remote station includes an impedance element in circuit with its operating winding to eliminatetherefrom alternating current of magnitude adequate to energize the relay, but which impedance is vnot effective to limit direct current from energization of said relay. l'n conjunction with said relay, the transfer switch, which is polarized for selective'operation depending upon the polarity of the direct' current applied thereto, may be utilized at the remote station to change connections as desired, as for example for reversing the direction" of'rotation oi a motor.

The relay is so connected in circuit with the operating winding of the transfer switch that that winding may not be energized except upon application thereto of direct current. The relay also functions to open the circuit tothe remotely controlled device, such' as the motor, to prevent application thereto of the direct current. Unwanted` application to the controlled device of control current is thus prevented.

By reason oi the foregoing provisions, positive and effective control of the transfer switch is obtained, and the invention has the further advantage that the system is particularly well suited to` applications such as cranes and trains, where the receivingv station may move relative to the control station. Thus, in the operation of miniature trains, the driving motor of the locomotive may be reversed at will by operation of the selector switch, momentarily to apply direct current between the two current-carrying rails to operate the transfer switch from one circuit-controlling position to another, as may be desired.

For further objects and advantages of the invention, reference is to be had to the following detailed description taken in conjunction with th-e accompanying drawings, in which:

Fig. l diagrammatically illustrates a wiring diagram of a preferred embodiment of the invention;

Fig. 2 diagrammatically illustrates a modication of the invention;

Fig. 3' is a'fractio-nal wiring diagram of a further modification of the invention; and

Fig. 4 diagrammatically illustrates a modification` of the selector switch which may be utilized at the control station.

Referring to the drawings, the invention in one form has been shown as applied to the control of a motor it?V illustrated as of the series type and including an armature Ia and a series field winding Ib which may be reversed at will by operation of a contactor such as a change-over switch or a transfer switchV Il under the control of a relay i2 and a selector switch I3. The motor l0 may be utilized for driving cranes or miniature trains or for other purposes where it is desired to control the motor at a distant location from a control station.

Though any suitable type of selector switch may be util-ized, the one illustrated in Fig. 1 is of the rotary type in which the ends of opposite spokes or the ends of a diametrically extending member 13j of insulating material has secured thereto l conductive segments i3d and I3e. The `diametral member i 3f is shown in a position completing circuits through stationary contacts I3b and I3b and when rotated in one direction or the other will complete circuits respectively through stationary contacts I3a, I3a and through stationary contacts I3o, I3c. With the selector switch and the other parts in the positions shown in Fig. 1, the motor I Il will be energized through a circuit which may be traced as from the lefthand supply line I4 through contacts I3b and I3e, conductor I5, terminal I'I, contacts II a and I Ii of the transfer switch II, field winding IIlb, the contacts IIc `and IIy', motor armature IDa, relay contacts I 2a and I2b, terminal I8, conductor I6 and by way of selector contacts I3d and I3b to the other supply line I4. Thus, the motor is energized for rotation in one direction, as for example, driving a locomotive of a miniature train forwardly along a track.

For the purposes of brevity and clarity, the movable contacts I3d and I3@ of selector switch I3 will not be recited for each switch connection. Reference to the stationary contacts alone, being shorted by movable contacts I3d and I3e in any described position, will describe the connecting action of selector switch I3.

For the train application, it will be frequently desirable to reverse the motor with the train at any location in a network of tracks. In accordance with the invention, the reversal of the motor will be achieved by using a handle or knob to rotate the selector switch I 3 to interrupt the circuit by way of contacts I3b-I3b and to complete a control circuit to conductors I5 and I 6 by way of stationary contacts I 3c-I3c from supply conductors I9 and 20 connected to a source of direct current. It will be observed that the control circuit for the operating coil of the relay I2 may be traced by way of supply line 20, stationary contacts I3c, conductor I6, terminal I8l operating coil of relay I2, impedance 2I which is characterized by its high reactance to alternating current and its low impedance and low ohmic resistance to direct current, and by way of terminal I'I, conductor I5 and stationary contacts I3c to the other direct-current supply line I9. The relay I2 is immediately energized to interrupt the motor circuit through contacts I2a and I2b and to complete a circuit through contact I2c for an actuating coil IIh of the operating winding of the transfer switch II.

In Fig. 1, coil I Ih is in circuit with a unidirectional conductive device I If. At this point it may be emphaszed that the selective operation of the transfer switch I I is made dependent not only upon actuation of relay I2, but also upon the polarity of the direct current applied to the single pair of conductors I5 and I6 by inclusion in the control circuits of the unidirectional conductive devices II e and II f which may comprise copperoxide rectiers. Thus, the energizing circuit for an -actuating coil IIh of transfer switch II may be traced from supply line by way of stationary contacts I3c, conductor I 6, terminal I8, relay contact I2b and control contact I2c, unidirectional conductive device I If, actuating coil I I h, terminal I1, conductor I5 and by way of stationary contacts I3c to the other direct-current supply line I9. The actuating coil I Ih is immediately energized to operate the armature or core of transfer switch II to move segment II i between contacts IIb and to move segment IIy' between contacts I Id. Accordingly, the power circuit for the field winding IIlb of motor I0 is reversed by the foregoing operation of the transfer switch I I preparatory to completion of the power circuit from alternating-current supply conductors I4. Power is applied to motor Ill for reverse operation by returning the transfer switch I3 to the position shown in Fig. l. Upon interrupting the circuit from direct-current lines I9 and 20, the relay I2 is immediately deenergized, the contact I2b completing a circuit through stationary contact I2a. Thus, as the selector switch is returned to the illustrated position, power flows through the previously traced circuit and by way of terminal Il through stationary contacts IIb now bridged by segment IIz, field winding lill? in a direction opposite to that previously traced, thence by way of stationary contacts IId now bridged by segment IIy', and by way of the relay contacts and terminal I8 to the other source of supply. It is to be observed the armature Ic of motor I0 is energized from the same circuit, but the direction of current therethrough is the same as before. In this manner the motor is energized for reverse operation to reverse the movement of the train or to produce the desired control action at the remote station.

At any time it is desired again to reverse the operation of motor I0, as by actuation of the transfer switch I I to the full-line position shown in Fig. 1, it is only necessary to rotate the selector switch I3 in a counterclockwise direction to complete circuits through stationary contacts I 3a and I3a'. As before, the relay I2 is immediately energized by application of direct current to interrupt the circuit through power contact I2a and to complete a circuit through stationary control contact I 2c which, by reason of the reversed polarity of the unidirectional current from lines I9 and 2li, is effective through the unidirectional conductive device IIe to energize actuating coil IIg to return the transfer switch II from the broken-line position shown in Fig. l to the fullline position thereof. Return of the selector switch I3 to the power position shown in Fig. 1 interrupts the energizing circuit for relay I2 and completes the power circuit for rotation of motor II) in the forward direction.

While a preferred embodiment of the invention has been described, it is to be understood that modifications may be made within the scope of the appended claims as by way of additions such as a line switch and circuit in either or both of supply lines I4 and direct-current lines I9 and 20 and by way of substitute or equivalent devices which introduce added functions into the operation.

For example, in Fig. 2 the transfer switch II has been illustrated as comprising a pair of circuit controllers IIt and IIu of the latched-in type. As will be explained in detail, they have the advantage of preventing energization of the actuating coil when the selector switch is moved to a position for actuation of one of the latchedin circuit controllers or contactors which has already been moved to an energized position. Thus, the selector switch can then be used for an onand-oif switch without continued energization of an actuating coil of the transfer switch. The use of latched-in contactors also has the advantage of being readily available on the market at reasonably low cost and of assuring freedom from adverse effects due to shock and the like.

Referring now more particularly to Fig. 2, it will be observed that the operating coil I Ig is connected in circuit with contacts IIlc of its associated contactor IIt, operating coil I Ih being similarly connected with respect to contacts Ilm of vits associated contactor IIu. Thus, as one contactor releases the other as by energization of trip coil il n or Ilp, the control circuit is partially completed, but after one of the contactors has been moved to a latched-in position, the control circuit is open.

In Fig. 2 the power circuit through the selector switch I3 is the same as in Fig. l, but from terminal I'I is traced through power contacts IIa of contacter IIt by way of motor eld coil Illb, power contacts I Ic of contactor I It, motor armature Illa, and by way of relay power contacts I2a to the other terminal I8. It is to be observed that contacts IIlc are in open-circuit position, the contactor IIt being held in its latched-in position by the latch actuated by the releasing coil IIn. Accordingly, if selector switch I3 be rotated in a counterclockwise direction to complete circuits through stationary contacts I3a, I3a, the relay I2 will be energized by flow of unidirectional current through impedance 2 I, but the operating coil Iig will not be energized since that circuit including tripping coil I Ip and actuating coil I lg is open by reason of the open-circuit condition of control contacts I Ik. Thus, the selector switch I3 can be operated between its illustrated position and its first counterclockwise position as an onand-off switch for the motor I0.

In order to reverse the operation of the motor il), it is only necessary to operate the switch i3 in a clockwise direction to complete circuits through stationary contacts I3c and |30', the result of which is to energize the relay l2 and to complete an energizing circuit as from terminal I8 by wayof relay control contacts I2C, unidirectional device Ilm, operating coil Ilh, and by way of trip coil i In to the other terminal I'I. Thus, the latchedin contactor IIt will be tripped to open the circuit through its power contacts IIa and I Ic and to complete a control circuit through interlock l will be observed the energizing circuit for its actuating coil IIh. and for the tripping coil Ill-n is interrupted' through interlock control contacts I- I m. Hence, the selector switch I2 may be used as an on-and-oir control switch when rotated between the illustrated power position and the control position bridging contacts I-3c and Ito'.

Instead of transfer switches of the type illustratedv in Figs. l and 2, a transfer switch of a somewhat simpler design may be utilized as illustrated in the modification of Fig. 3 and which comprises magnetic structure of the polarized type. As shown in Fig. 3, such a transfer switch II has been illustrated as connected to terminals I-'I and I8, the remainder of the control circuit being the' same as in Fig. 2l and being omitted in Fig. 3. As shown, power may ow as, for exam-ple, from terminal I'I through stationary contact Ha, eld coil Mib, contact I Ic and by way of motor armature I-Ua, and relay contacts I2a and I 2b-to the other terminal I8. Sincey the magnetic structure of transfer switch II of Fig. 3' is polarized, application toterminals I-'I, and. I8. of unidirectional current` of, one polarity will not cause movement of the movable contacts IIq and II`r, but appli- IIf, interlock control contact I cation of 'unidirectional current of reversed polarity will cause such contacts to move to their illustrated broken-line positions, thereby reversing the connections to motor field winding IUb to reverse the motor. The relay I2 functions as before in response to the application of unidirectional current to interrupt the power circuit and to complete the control circuit to the operating winding Ils of polarized transfer switch II.

It is to be understood that several electrical switches can be utilized to complete circuits to the pair of conductors I5 and I6 and that the selector switches may differ in construction so long as they perform the circuit-controlling functions which have already been set forth in detail. For example, the selector switch may be constructed as illustrated in Fig. 4, the switch handle I3g having three positions a, b` and c, respectively corresponding with movable contact |311 in engagement with stationary contact |311, I3b or 13o. More particularly, if the knob or operating arm I3g of selector switch I3 of Fig. 4 be rotated from position a to position b, movable contacts i3d and 13e engage stationary contacts i317 and lsb' to complete a circuit from alternating-current supply lines I4 to conductors I5 and i-'o and to already described power circuits in a remote station or in a number of such remote stations.

Reversal of connections to the motor can be made by moving handle I3g from position b to position c, whereupon control voltage of a polarity opposite to that applied when the switch was in position a will be applied to conductors I5 and i6, As already described, the application of this control voltage of reversed polarity actuated the relay and transfer switch of a remote station to change power connections for reverse operation of a power-consuming device. vSubsequent movement of knob I3g to position a applies the control voltage of the other polarity and will thereby actuate the relay and transfer switch of the remote station to return power connections to the original operating position.

What is claimed is:

l. A control system comprising a transfer switch having selectively positionedy power contacts determining the sense of power applied through them and actuating means, a relay having control contact structure operable to a position in circuit with the actuating means of said transfer switch and having power contact structure operable to a position in circuit with the power contacts of said transfer switch, a' selector switch having at least two control positions and a power position and connected to theoperating coil of said relay, means including interconnectionl between the control contact structure of said relay and. the actuating means of said transfer switch controlled byA movement of saidY selector switch to a control position for selectiver positioning of the power-contacts ofl said transfer switch, and meansr including interconnection' betweenl the power contacts controlled by movement ofV the'selector switch to powerpo'sitionv and those of saidA transfery switch for" application of power in thesense preset by the prior selected control position of the selector switch.

2. A control system for electrical power comprising a three-position selector switch, a twoposition relay, a single pair of conductors. exf tending between said selector switch and said relay, said selector switch in a rst position applying to said. conductors electricalv energy of oneA character, in a second position applying power energy to said conductors and in a third position applying electrical energy of a different character to said conductors, a transfer switch at said relay location operable between forward and reverse positions, an operating winding for said transfer switch, said relay in its deenergized position completing a power circuit through said transfer switch and between said two conductors, circuit connections to said pair of conductors from the operating winding of said transfer switch completed by energization of said relay foroperating said transfer means, and means included in circuit vwith the operating winding of said transfer means for producing selective operation thereof upon movement of said threeposition selector switch to said first or to said third positions thereof to eect selected operation of said transfer means by the character of the control energy applied to said pair of conductors.

3. A control system comprising a transfer switch at a remote location having contacts operable between one circuit-controlling position and another circuit-controlling position, actuator means for said switch responsive to the character of control energy supplied thereto for selective control of the operation of said transfer switch, a relay having a contact which in one position of the relay completes a power circuit to said contacts of said transfer switch and hav- .Y

ing a. contact which for a second position of said relay completes a control circuit for said actuator means, a pair of conductors extending from said remote location to a control station, said relay having an operating coil connected to said conductors, means in circuit with said coil for preventing actuation of said coil by power energy and offering low impedance to flow of control energy to energize said relay to connect said actuator means to said conductors for operation of said transfer switch to a selected circuitcontrolling position, a selector switch at said control station in one position controlling the application of electrical power energy by way of said conductors and said relay to the contacts of said transfer switch, said selector switch in a second position applying electrical control power of a distinctively differing character to said conductors, said selector switch having a third position for applying control power of a still differing character for energizing said relay and said actuator means to operate said transfer switch to its other circuit-controlling position.

4. A control system for an electrical machine comprising a three-position selector switch connected to power-voltage supply lines and to oontrol-voltage supply lines, a two-position relay, an impedance element in circuit with said relay limiting the response of said relay to control energy, a single pair of conductors connecting said selector switch to said relay and impedance element in series connection, a transfer switch connected to said conductors and selectively responsive to control voltages and having an actuating circuit completed upon energization of said relay, said relay in its deenergized position completing a power circuit to the contacts of said transfer switch and to the electrical machine.

5. A control system for an electrical machine comprising a single pair of conductors between a control station and a remote station, switching means for selectively impressing a control voltage and a power voltage of different characteristics upon said conductors, a relay connected to said conductors and including means for precluding relay response to power voltage, said relay having control contacts and power'contacts for alternate connection to the rst of said conductors, a contactor having a control circuit in `circuit with the control contacts of said relay and having power contacts in circuit with the power contacts of said relay and having a common connection to the second of said conductors, said contactor including circuit connecting means whereby an operating condition'for the electrical machine is selected and power applied thereto, and polarized conductive means providing for selective response of said contactor to control voltages as impressed by said switching means.

6. A control system for electrical power comprising a two-pole, three-position selector switch having power contacts and control contacts for connection to power-voltage supply lines and to control-voltage supply lines; a single-pole, twoposition relay in circuit with said selector switch and having a power contact and a control contact for connection in circuit with the first pole of said selector switch; means in circuit with said relay for precluding response thereof to powervoltage; a contactor in circuit with the second pole of said selector switch and having actuating means and power contacts, said control contacts being in circuit with said control contact of said relay with said relay in one position and said power contacts being in circuit with said power contact of said relay and with a power-consuming device wi-th said relay in a second position; and polarized means for selective response of said contactor to control voltages of differing characteristics; said contactor being governed in its position by the combined action of said selector switch and said relay, and having circuit-connecting means whereby power is removed, either of alternate operating conditions selected, and power reapplied as determined by the positioning of said selector switch.

7. A control system for an electrical machine comprising a two-pole, three-position selector switch connected to power-voltage lines and to control-voltage lines, a single pair of conductors connected to the polar contacts of said selector switch, an impedance element connected to the first of said conductors and having a high reactance to power-voltage, a relay connected to the second of said conductors and to said impedance element, a first contact connected to the second 0f said conductors by said relay when energized, a second contact connected to the second of said conductors when said relay is deenergized, said second contact connecting to the electrical machine, a transfer switch having a plurality of actuators and a plurality of contacts connected to the rst of said conductors, said actuators connected to said rst relay contact for control actuation and said transfer-switch contacts being connected to said electrical machine for power and adapted to reverse connections thereto and to open actuator circuits after actuation, means in circuit with each of said actuators for latching it in position when actuated vand for releasing the other of said actuators, and unidirectional conductors in circuit with said actuators for selective actuation thereof.

8. A control system for an electrical machine comprising a three-position, two-pole selector switch connected to alternating-current supply lines and to direct-current supply lines, a single pair of conductors connected to the two poles of said selector switch, said supply lines beingcon- 9 nected to the three positions of each polein an arrangement providing one type of control voltage in the first position, power voltage in the second position, and a second type of control voltage in the third position to said pair of conductors; a two-position relay having an operating coil and contact circuits, said operating coil and contact circuits having a common connection to the first of said conductors and the iirst of said contact circuits connecting to said electrical machine when said relay is in the deenergized position; an impedance element connected to lthe second oi said conductors and in circuit with the relay operating coil and limiting the response of said relay to control energy; a contacter having a plurality of power contacts and control contacts and actuators therefor, said actuators being in circuit with means for latching an energized actuator in energized position and for releasing the t other actuator and with unidirectional conductors in opposite polarities for selective operation of said actuators and with said control contacts for breaking the control circuit through each actuator immediately after energization thereof, said latch-releasing means being commonly con.-

nected to the second of said conductors, said unidirectional conductors being commonly connected to the second of said relay contact circuits, and

said power contacts being in circuit with saidr conductors and said electrical machine so as to 'l -f control the operating condition of said electrical machine upon energization of said actuators.

9. A control system comprising a two-pole, three-position selector switch connected to supply lines for power voltage and to other supply lines for control voltage and having a pair of contacts common to all three positions thereof and having other contacts arranged at said three positions for connecting said -supply lines to said common contacts so as to provide control voltage of one characteristic in the iirst position, power voltage in the second position, and control voltage of a second characteristic in the third position; a pair of conductors connected to said pair of common contacts; a relay having an operating coil connected to a rst of said conductors and having contacts connected to said rst conductor, the first of said relay contacts being closed when the relay is energized and -open when it is deenergized, the second o1" said relay contacts being open when the relay is energized and closed when it is deenergized, an impedance element connected to the second of said conductors and to said relay coil and presenting a high value of reactance to said power voltage, whereby said relay is yoperalole only by control voltages; a transfer switch responsive to the combined action of said relay and of said selector switch and having` a plurality of contacts land circuit [connecting means for reversing the connection of a load circuit between said power voltage supply lines, a plurality vof actuators for closing said plurality of contacts, means for latching said actuators in closed position, means in circuit with each of said actuators adapted to release said latching means of the other actuator, said releasing means being commonly connected to the second of said conductors, and means in circuit with each of said actuators for opening its control circuit; and a plurality of unidirectionally conductive elements commonly connected to said first contacts of said relay and further connected one to each actuator circuit in opposed polarity so as to provide for selective energization of said actuators in response to changes in the characteristics of 10 the control voltages provided by said selector switch.

10. In an alternating-current power system, a direct-current system for remote control lcomprising a single pair of conductors extending from a control station to a distant station, a selector switch at th-e control station for applying direct current of either polarity or alternating current to said conductors, a direct-current responsive relay at said distant station in circuit with said conductors and including power contacts and control contacts and actuated by said selector switch, and a contacter in circuit with said relay contacts and with said conductors at said distant station and governed in its position by said selector switch and said relay and energized only when direct current is selected, whereby one yof a plurality of operating conditions is selected for said alternating-current power system as determined by the polarity of the applied direct-current.

11. A remote control system comprising a pair of conductors extending between a control station and a distant station, a power-consuming device at said distant station, means including a transfer switch having an operating winding and contact-s for varying the connections to said device, a relay having an operating coil, said relay in one position completing a ycircuit from said device to said conductors and in a second position completing a circuit from said conductors to the operating winding of said transfer switch, means in circuit with the coil of said relay for limiting alternating-current ilow therethrough below the pickup value of said relay, said impedance having low ohmic resistance for flow of direct current therethrough for operating said relay from one to the other of its positions, a selector switch at said control station operable in a first position for applying alternating current to said pair of conductors, said selector switch having second and third positions for application to said pair of conductors of direct current of selected atlernate polarities, said relay upon application of direct current interrupting said circuit to said device and completing a direct-current circuit to said operating winding of said transfer switch for operating the same from' one circuit-controlling position to another, return of said selector switch to said rst position returning said relay to its first position and applying to said conductors alternating current for flow to said device through said dierent circuit connections, said selector switch in said third position applying direct current of opposite polarity to said pair of conductors again to energize said relay and to operate said transfer switch again to change said circuit connections to said device for application thereto of said alternating current upon return of said selector switch to its said first position.

12. In a control system, a pair of conductors from a control station to a remote station, a relay connected to said conductors and responsive only to control voltages, a transfer switch having actuating means and circuit-controlling contacts connected to said conductors, said actuating means including polarized conductive means for selective response to diierent control voltages and said circuit-controlling contacts being operable by said actuating means from one circuit-controlling position to another circuitcontrolling position, and contacts in circuit between said conductors and said transfer switch and operable by Said relay, said contacts in one position of said relay completing a power circuit to the circuit-controlling contacts of said transfer switch and in a second position completing a control circuit to the actuating means of said transfer switch, whereby a circuit-controlling position is selected upon application of a control voltage to said pair of conductors and a power circuit is completed upon application of power voltage to said pair of conductors.

13. A remote control system for electrical power comprising a contactor having actuators, power contacts, and control contacts in circuit with said actuators; a relay including a power contact and a control contact and operable to one position to connect its power contact in circuit with the power contacts of said contactor and operable to a second position to connect its control contact in circuit with the control contacts of said contactor, and an operating coil, an electrical device in circuit with said coil for making it respond only to control energy; switching means connected to the operating coil of said relay and connected in circuit with the control contacts of said relay and of said contactor for selectively impressing control voltages of diiering characteristics and power voltage on said relay and said contactor; and polarized means in circuit with said actuators and providing for selective response of said contactor to control voltages of differing characteristics.

14. In a control system for an electrical power-consuming device, a remotely controlled station comprising a, polarized relay having contacts operable from one circuit-controlling position to another circuit-controlling position and having actuator means responsive to the character of control energy supplied thereto for selective control of said contacts, a second relay having a contact which in one position of the second relay completes a power circuit through the power-consuming device to the contacts of said polarized relay and having a contact which in a second position of the second relay completes a control circuit for the actuator means of said polarized relay, a pair of conductors extending from the remote station to a control station, said second relay having an operating coil connected to said conductors, and means in circuit with said operating coil preventing actuation of said second relay by power energy and offering low impedance to ow of control energy to energize said second relay to connect said actuator means to said conductors for operation of said polarized relay to a, selected circuit-controlling position.

THOMAS L. STURGEd REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Number NameV Date 1,140,545 Townsend May 25, 1925 1,873,579 Haas Aug. 23, 1932 2,018,818 Thompson Aug. 29, 1935 2,250,214 Ashworth July 22, 1941 2,365,641 Jerome Dec. 19, 1944 2,495,791 Van Daele Jan. 31, 195.() 

